Apparatus and method for X-ray fluorescence imaging

Abstract

Apparatuses and methods of X-ray fluorescence (XRF) imaging use a radiation source to stimulate XRF from only a slice of an object by projecting a radiation beam through only the slice. An X-ray detector having a plurality of pixels is provided. A collimator having a plurality of parallel collimator plates is positioned between the object and the X-ray detector. The radiation beam is not parallel to the collimator plates. Neighboring pairs of the collimator plates allow XRF from only respective portions of the slice to reach respective subsets of the pixels. For each of the respective pixel subsets the X-ray detector sums signals generated in the pixel or pixels of the respective subset. The radiation beam is a fan beam or a pencil beam. A pixel pitch of the X-ray detector is an integer multiple of a plate pitch of the collimator.

What is claimed is: 
     
         1 . An apparatus comprising:
 a radiation source configured to stimulate X-ray fluorescence from only a slice of an object by projecting a radiation beam through only the slice;   an X-ray detector having a plurality of pixels; and   a collimator having a plurality of parallel collimator plates, wherein the radiation beam is not parallel to the collimator plates,   wherein neighboring pairs of the collimator plates allow fluorescent X-ray from only respective portions of the slice to reach respective subsets of the pixels, and   wherein, for each of the respective pixel subsets the X-ray detector is configured to sum signals generated in the pixel or pixels of the respective subset.   
     
     
         2 . The apparatus of  claim 1 , wherein the slice has a lateral size narrower than the object. 
     
     
         3 . The apparatus of  claim 1 , wherein the radiation beam is an X-ray beam or a gamma ray beam. 
     
     
         4 . The apparatus of  claim 1 , wherein the parallel collimator plates are spaced apart uniformly, the spacing of the parallel collimator plates being characterized by a plate pitch, and
 wherein the pixels are spaced apart uniformly, the spacing of the pixels being characterized by a pixel pitch that is an integer multiple of the plate pitch.   
     
     
         5 . The apparatus of  claim 1 , wherein each pixel of the plurality of pixels is configured to count numbers of X-ray photons incident thereon. 
     
     
         6 . The apparatus of  claim 5 , wherein each pixel is further configured to count numbers of the X-ray photons incident thereon whose energy falls in a plurality of bins, within a period of time; and
 wherein the apparatus is configured to add the numbers of X-ray photons for the bins of the same energy range.   
     
     
         7 . The apparatus of  claim 1 , further comprising:
 a specimen fixture to hold the object; and   the specimen fixture is substantially transparent to the radiation beam and XRF.   
     
     
         8 . The apparatus of  claim 1 , wherein the parallel collimator plates contain at least one element that absorbs X-ray. 
     
     
         9 . The apparatus of  claim 8 , wherein the parallel collimator plates contain at least one element from among the group consisting of lead, tungsten, and gold. 
     
     
         10 . The apparatus of  claim 8 , wherein the collimator further includes
 a filler that fills all or part of at least one gap between the parallel collimator plates, and   the filler is substantially transparent to X-ray.   
     
     
         11 . An X-ray fluorescence imaging method, comprising:
 providing an X-ray detector having a plurality of pixels;   projecting a radiation beam through a slice of an object to stimulate XRF from the slice; and   allowing XRF from only respective portions of the slice to reach respective subsets of the pixels by providing between the object and the X-ray detector a collimator having a plurality of parallel plates not parallel to the radiation beam, wherein each pixel of each subset of pixels is aligned to receive XRF between only one neighboring pair of the parallel plates; and   counting numbers of XRF photons incident on each pixel of the X-ray detector.   
     
     
         12 . The method of  claim 11 , further comprising:
 counting numbers of the XRF photons incident on each pixel whose energy falls in a plurality of bins, within a period of time; and   adding the numbers of XRF photons for the bins of the same energy range.   
     
     
         13 . The method of  claim 11 , further comprising:
 resolving an image of the object in a first direction orthogonal to a primary axis of the radiation beam based on a size of the slice in the first direction; and   resolving the image of the object in a second direction orthogonal to the primary axis and orthogonal to the first direction based on a size of a gap between neighboring pairs of the parallel plates.   
     
     
         14 . The method of  claim 13 , further comprising:
 resolving the image of the object in a third direction orthogonal to the primary axis and orthogonal to the first and second directions based on a size of the slice in the third direction.   
     
     
         15 . The method of  claim 11 , further comprising:
 projecting the radiation beam through a first slice of the object;   counting the numbers of XRF photons incident on each pixel of the X-ray detector from the first slice;   projecting the radiation beam through a second slice different from the first slice; and   counting the numbers of XRF photons incident on each pixel of the X-ray detector from the second slice.   
     
     
         16 . The method of  claim 15 , wherein the object is stationary, and the radiation beam is moved. 
     
     
         17 . The method of  claim 15 , wherein the radiation beam is stationary, and the object is moved. 
     
     
         18 . The method of  claim 15 , further comprising:
 moving the radiation beam in a first scanning direction from a first position where the radiation beam projects through the first slice to a second position where the radiation beam projects through the second slice.   
     
     
         19 . The method of  claim 18 , wherein the moving the radiation beam includes translating the radiation beam. 
     
     
         20 . The method of  claim 18 , wherein the moving the radiation beam includes rotating the radiation beam.